The invention relates generally to testing the resolution of an electron beam lithography tool, and more specifically to a method and patterns for efficiently evaluating the resolution.
Currently, the resolution of a lithography tool is measured by exposing a test pattern that is designed for a particular set of critical dimension (CD) measurements. Critical dimension measurements represent the smallest feature size (i.e., line or space width) obtainable from a lithographic process. However, the resolution test pattern is often not designed to provide insight to the lithography tool factors that limit performance. As a result, a separate set of exposures of specialized patterns may be required to determine which exposure conditions of lithography tool must be adjusted to improve the resolution. Exposure conditions that are typically adjusted include focus coil excitation, stigmator corrector excitation, and beam exposure time. Once the lithography tool performs at a desired level, the resolution test pattern will be exposed again for final verification.
However, the current process wastes both lithography tool time as well as space in the test patterns. For example, a test pattern may comprise several groups of interleaved lines and spaces (i.e., “finger arrays”) for measuring the resolution of the lithography tool. While such a test pattern allows for thorough testing of various combinations of line and space widths, additional test patterns must be exposed to effectively analyze other feature types (e.g., contact holes).
As a result, a need exists for improved test patterns that more efficiently evaluate the resolution of a lithography tool and provide the information necessary to improve the resolution. Further, a need exists for an improved method of evaluating and adjusting the lithography tool using these test patterns.